Two Heads are Better than Two
نویسندگان
چکیده
We show that a Turing machine with two single-head one-dimensional tapes cannot recognize the set f x2x 0 j x 2 f0;1g and x 0 is a preex of x g in real time, although it can do so with three tapes, two two-dimensional tapes, or one two-head tape, or in linear time with just one tape. In particular, this settles the longstanding conjecture that a two-head Turing machine can recognize more languages in real time if its heads are on the same one-dimensional tape than if they are on separate one-dimensional tapes.
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